Discussion of Public Participation Online Trail Databases

New - The details of the network
algorithm and other issues related to trail databases are
published in the 2004 JCDL conference proceedings. The paper is also
available from TopoFusion and is entitled Digital Trail Libraries (5 MB, pdf
format).

There is at present a growing need for current and accurate trail
information. Those who visit natural areas know that good trail
information is frequently scarce. Maps grow quickly out of date as
trails are closed or re-routed. Often the land managers themselves
have little or no trail data. There is also no standard for trail
data.

With the advent of inexpensive consumer level GPS technology, a new
possibility for collection of current and accurate trail data has
presented itself. What better source of data than those who are
actually using the trails? There are several advantages to this
approach, foremost of which is the advantage in the accuracy of the
GPS data itself.

We consider a central database of user submitted GPS data. GPS data,
in this case, consists of GPS track logs. A track log is a single
trip recorded in the field by a trail user. The GPS device maintains
a position lock throughout the trip and records positions information
(a bread crumb trail) at intervals. The GPS track is then downloaded
to a computer, optionally cleaned up by hand, and submitted to the database.

Allowing user submissions of GPS data gives rise to a few major
problems. First, different trail users can submit the same trails.
This could be avoided by simply not allowing duplicate submissions, requiring
the user or the database manager (a person) to enforce this. However, we will see
how duplicate submissions can actually be of benefit.

User tracks can also overlap other tracks only partially.
Imagine that a user travels ten miles on trails that are already found in
the database but then branches off to a trail not in the database. This again
could be taken care of by not allowing duplicates. But users are interested
in logging their entire trip, not just a new portion. Requiring them to hand
edit out portions is also undesirable. Instead, we would like an automatic method
for combining GPS tracks which detects and eliminates duplicate tracks.
The problem, then, goes from representing single tracks (a
single trip) to representing whole networks of trails.

Another issue is one of data reliability. If anyone is allowed to submit data there is nothing
to prevent submission of bogus tracks. Since it is impossible to verify whether trails
submitted actually exist, some sort of reliability measure must be taken into account. Here
is one of the reasons that multiple submissions of the same trail is desirable. Each trail
segment can be annotated with the number of submitted tracks that cover this segment. Segments
with a high number of (unique user) submissions can most likely be relied upon. Further, a
user ranking system could also be employed, so that submitters of erroneous data can be
penalized.

The other advantage of obtaining multiple submissions for identical trail segments
lies in the accuracy of the data. GPS errors can be corrected for by averaging
the segments together. The result will be a better representation of trails. Our hope is
to obtain accuracy results equivalent to expensive DGPS (differential GPS) by averaging
consumer level GPS tracks together.

Therefore, it is our view that developing automatic methods for
collecting and classifying user submitted trail data is essential.
One of the primary reasons for creating TopoFusion is to serve as a testbed for network
GPS algorithms.

We are working on solving these and other GPS data related
problems. Specifically, we have designed and implemented an algorithm
that, given multiple GPS tracks as input, will produce a network (a
graph) that represents each unique trail as a single trail segment.
It also averages tracks together to produce a more accurate
description of the trail(s).

To see and play with our GPS network algorithm, check out the
demonstration version of TopoFusion. It's
available free.

For example networks produced by the algorithm, see our GPX Networks. The networks are available in GPX
format, an open standard for exchange of GPS data.

Check out trailregistry.com, a
user-submitted database of hiking trails. Geoff has done some great
work on a web interface to detailed trail data, all in GPX format! He
uses some heuristics to separate trails at there intersection points
so that new trips can be planned, similar to TopoFusion's
networks.

Also check out Crankfire.com a
nice site incorporating user submission of trails for Conneticut.

Singletracks.com is one of the best
examples of user submitted, manually edited trail databases. It's going to be
great to see this collection of data flourish.

And, Water Trails - User-edited water
trails for kayaks and canoes in the San Francisco Bay Area

Application to Recreation Simulation

Besides being of benefit to trail users and land managers, we hope
such a database of recreational trails will be useful for trail user
simulation, conflict management and resource allocation. Agent based
modeling approaches to recreation management are becoming increasingly
popular. A key problem to applying trail user simulation in a
widespread manner is the lack of accurate and current trail data.
Often this data must be collected and classified by hand. A database
of submitted trails would solve this. Modelers would also have the
advantage of usage statistics on trails. Further, precise speed and
elevation data can be extracted for use in the simulation.

Herein lies another advantage of the trail network algorithms. Agent
based simulations require a network of trails--not unconnected trail
segments. The topology of the network must be present, which is
exactly what a GPS network algorithm will produce.

We are
currently implementing agent based modeling of trail users in
TopoFusion. For more information on this part of the project, please
see Trail Simulation.

Contact Us

We are intersted in hearing from anyone interested in these or related problems.
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